The constellation Hercules (pronounced HER-cue-leez) is one of the original star figures created by the Greeks, who called the hero Herakles. The main part of the pattern is reasonably easy to find. It’s visible from mid-spring through mid-fall in the Northern Hemisphere. Its center lies at R.A. 17h21m and Dec. 27°30′.
Hercules ranks fifth in size out of the 88 constellations, covering 1,225.15 square degrees (2.97 percent) of the sky. And while its size places it near the top of that category, it fares worse (48th) in terms of overall brightness.
The best date to see Hercules is June 13, when it stands opposite the Sun in the sky and reaches its highest point at local midnight. The constellation is completely visible from latitudes north of 39° south and totally invisible only south of latitude 86° south.
Although this star pattern isn’t bright, it contains two Messier objects, both globular clusters: M13 and M92. You’ll find lots of other worthy targets, too. Let your telescope adjust to the outside temperature, get comfortable, and spend an enjoyable night leisurely making your way through the many great deep-sky objects residing in Hercules. Good luck!
The Hercules Galaxy Cluster (Abell 2151) lies at the astounding distance of 500 million light-years from Earth. Abell 2151 requires at least a 12-inch telescope and eyepieces that give powers in excess of 250x. Target its brightest member, the elliptical galaxy NGC 6041, which glows at magnitude 13.4.
Adam Block/Mount Lemmon SkyCenter/University of Arizona
The Hercules Cluster (M13) is the standout deep-sky treat in this constellation. It glows at magnitude 5.8 and has a diameter of 24′. Under a dark sky, you’ll spot it with your naked eyes two-thirds of the way from Zeta (ζ) to Eta (η) Herculis. Through 8-inch and larger scopes, you’ll see hundreds of stars.
Once you’ve found M13, look ever-so-slightly less than 0.5° northeast for spiral galaxy NGC 6207. Many low-power eyepieces show both objects in the same field of view. Through an 8-inch telescope, you’ll see a magnitude 11.6 oval a bit more than twice as long as it is wide.
The Turtle Nebula (NGC 6210) is a planetary nebula that measures 14″ across. But even through a small telescope, you can easily identify this planetary’s light blue-green, turtle-shaped, magnitude 8.8 disk. Its high surface brightness lets you really crank up the magnification.
Martin C. Germano
Globular cluster NGC 6229 glows at magnitude 9.4 and measures 4.5′ across. At low to medium magnifications, you’ll see a nice triangle formed by the cluster and two 8th-magnitude stars. NGC 6229 is 100,000 light-years away, so an 8-inch scope shows just an unresolved glow with an irregular outline.
Rasalgethi (Alpha [α] Herculis) is a binary that combines stars with magnitudes of 3.5 and 5.4. They’re separated by 4.6″. Because of a wonderful contrast effect, the secondary appears olive-green. The brighter primary is yellow with a trace of orange.
Globular cluster M92 is this constellation’s other Messier object. It has a diameter of 14′ and a magnitude of 6.5. Nearly as bright as M13, M92 easily resolves with small telescopes. Through an 8-inch scope, the core appears concentrated and huge, surrounded by an outer halo of myriad faint stars.
The stellar pair called 95 Herculis lies in a no-man’s land where few bright stars abound. One way to locate it is to look a bit more than 13° northeast of Rasalgethi. The (barely) brighter of these two stars (magnitude 5.0) glows yellow, and its companion (magnitude 5.1) is white.